Conservation of Vieira’s titi monkey 841
TABLE 1 Survey effort, number of sightings, sighting rates and density estimates (per ha) for Vieira’s titi monkey Plecturocebus vieirai obtained during 3 years (2016–2018) of systematic transect surveys in the southern part of the species range, Cláudia and Sinop municipalities, Mato Grosso State, Brazil.
Groups Locality1
Fazenda da Madenorte
Fazenda do Balin
Survey effort (km)
Rio Roquete Pinto 02 237 Tucunaré Total
336 306 313
1,192 1Locality names as per Supplementary Table 2.
TABLE 2 Extent of occurrence, suitable habitat, suitable habitat in protected areas and forest cover for P. vieirai in 2020 and after three P. vieirai generations (2044), with actual (2020) or predicted habitat loss (2044).
Variable
Extent of occurrence (km2) Suitable habitat (km2)
Forest cover (km2)
1Relative to original forest cover in 1985. 2Relative to suitable habitat.
150–410maltitude and within the boundaries ofAmazonian forests of the Tapajós domain, except for three records that fall within the boundaries of the Cerrado (Instituto Brasileiro de Geografia e Estatística, 2019) but were obtained in the Amazonia–Cerrado ecotonal forest (Silva et al., 2019). We also gathered a newrecord of Plecturocebusmoloch on the north bank of the Cristalino River (9.552926°S, 55.928568°W; Fig. 2), which is the southernmost documented record of this species in the Tapajós–Xingu interfluve and helped us to delimit the geographical distribution of P. vieirai,which is expected to occur on the opposite bank of the river according to our modelling (see below). Our combined results from habitat modelling and occur-
rence records show that P. vieirai occurs in an area of 226,054 km2 and is limited in the east by the Xingu River, in the north by the Irirí River, in the west by the Irirí, Cristalino and Teles Pires rivers and extending southwards to the upper Teles Pires and Xingu rivers (Fig. 2). The linear transect surveys totalled 1,192 km of trails walked, with 78 group encounters and 86 individuals observed in the four areas, resulting in a mean density of 0.03 groups/ha and 0.07 individuals/ha (Table 1), with mean group sizes ranging from 1.5 (95%CI 1.0–4.2)to 2.62 (95%CI 2.13–3.23).
2020 226,054
113,765 (56%)1
Suitable habitat in protected areas (km2) 66,142 (58%)2
148,096 (73%)1
29,381 (14%)1
25,763 (88%)2
60,731 (30%)1
2044 Considering the data on past and projected future forest
cover (Soares-Filho et al., 2006; Souza et al., 2020) and our new range delimitation for P. vieirai,in 1985 forests covered 90% of the range of P. vieirai (204,191 km2) but in 2044 only 30%(54,731 km2) of these forests will remain. Our modelling shows that suitable habitat (Table 2) for P. vieirai is currently 56% of the original area and that 58% of this is within protected areas and Indigenous lands. By 2044, according to our model, only 14% of the original P. vieirai habitat will remain, 88% within protected areas and Indigenous lands. We found that variables related to rainfall (specifically the
wettest quarter and the driestmonth) explain 60%of the like- lihood of P. vieirai occurrence (AUC= 0.999,TSS = 0.996) and therefore these variables are the best indicator of habitat suitability for this species (Supplementary Table 3).
Discussion
Our findings indicate that habitat loss as a result of conver- sion of forest into large-scale agriculturalmonocultures and pastures for cattle ranching is the main threat to P. vieirai. Ourmodel showed that because of deforestation the habitat of P. vieirai has been reduced by 56% and only 14% will remain by 2044. We expect a concomitant decline in the population size of P. vieirai. We assess P. vieirai to be Critically Endangered (Costa-Araújo et al., 2022) based on IUCN criterionA3bc (IUCN, 2019), given that our estimates suggest a projected population size reduction of $ 80% within the next three P. vieirai generations (A3), and that these estimates are based on an index of abundance that is appropriate for the taxon (b) and a decline in the area of occupancy of .80% (c). Additionally, decreases in the suitability of any remain-
ing habitat because of climate change compound the threats to the long-term survival of P. vieirai. Greenhouse gas emissions from human activities are causing extended dry seasons, increased frequencies of droughts and forest fires
Oryx, 2022, 56(6), 837–845 © The Author(s), 2022. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S003060532100171X
Number of sightings
26 15
15 22 78
Sighting rate/10 km
0.77 0.49
0.63 0.70 0.65
Density/ ha
0.03 Individuals
Number of sightings
42 12 26
6 86
Sighting rate/10 km
1.25 0.39
0.25 0.83 0.72
Density/ ha
0.07
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